Fuel fractionation method and fuel fractionation apparatus for internal combustion engine

ABSTRACT

A fuel fractionation method which can suitably control a state of a fuel at a time of fractionating the fuel in an internal combustion engine, which comprises the steps of applying an operation for promoting a fractionation of a fuel of an engine to a fractionation passage while making the fuel flow to the fractionation passage, thereby fractionating the fuel into a gas phase fuel and a liquid phase fuel within the fractionation passage, conducting the fractionated gas phase fuel and the fractionated liquid phase fuel to a branch point of the fractionation passage, and separating the gas phase fuel and the liquid phase fuel to a gas phase passage and a liquid phase passage, respectively due to gravity.

TECHNICAL FIELD

The present invention relates to a fuel fractionation method and a fuelfractionation apparatus for an internal combustion engine.

BACKGROUND ART

There has been known an exhaust gas purifying apparatus which heats afuel accumulated around an exhaust pipe of an internal combustion engineby an exhaust heat so as to fractionate the fuel into a light componentin a gas phase and a heavy component in a liquid phase, and supplies thefractionated light component as a reducing agent to an NOxocclusion-reduction type catalyst so as to reduce the NOx discharged bythe catalyst (refer to JP 3093905 B). In addition, there arepublications of JP 2850547 B, JP 11-210447 A and JP 2001-193525 asdocuments related to the present invention.

DISCLOSURE OF THE INVENTION

In the conventional apparatus mentioned above, since a lot of fuel isaccumulated around the exhaust pipe, a fuel temperature responds poorlyto an exhaust gas temperature change, and there is a case where it ishard to control the fuel temperature in a temperature range suitable forthe fractionation. Further, when the fractionation temperature isimproper, the light component is not vaporized or the heavy component isvaporized, whereby the light component and the heavy component aremixed.

Accordingly, an object of the present invention is to provide a fuelfractionation method and a fuel fractionation apparatus for an internalcombustion engine which can easily and rapidly control a fuel to a statesuitable for a fractionation so as to separate the fuel into a lightcomponent and a heavy component.

To achieve the object mentioned above, there is provided a fuelfractionation method for an internal combustion engine comprising thesteps of: applying an operation for promoting, a fractionation of a fuelof the internal combustion engine to a fractionation passage whilemaking the fuel flow to the fractionation passage, thereby fractionatingthe fuel into a gas phase fuel and a liquid phase fuel within thefractionation passage; conducting the fractionated gas phase fuel andthe fractionated liquid phase fuel to a branch point of thefractionation passage; and separating the gas phase fuel and the liquidphase fuel to an upper branch passage and a lower branch passage,respectively due to gravity.

According to the fuel fractionation method of the present invention,since the operation for promoting the fractionation is applied to thefractionation passage while making the fuel flow to the distributingpassage, a response of the fuel to the operation for promoting thefractionation becomes sensitive in comparison with the case offractionating a lot of fuel accumulated in a certain position all atonce, and it is possible to easily and rapidly control the fuel to astate suitable for the fractionation.

Further, since the gas phase fuel and the liquid phase fuel areseparated into the different branch passages respectively from thebranch point by utilizing a difference in a specific weight between thegas phase fuel and the liquid phase fuel, a separation of thefractionated gas phase fuel and liquid phase fuel can be achieved by asimple structure. In this case, the operation for promoting thefractionation is typically achieved by heating, however, the otheroperations than the heating operation can be employed as far as theoperation can promote the vaporization of the fuel.

To achieve the object mentioned above, there is also provided a fuelfractionation apparatus for an internal combustion engine comprising: afractionation passage which is connected to a fuel supply system of theinternal combustion engine and reaches a branch point in a terminal endthrough a fractionation section to which a fractionation promotingeffect of a fuel is applied; a liquid phase branch passage which isbranched to a lower side from the branch point; and a gas phase branchpassage which is branched to an upper side than the liquid phase branchpassage from the branch point.

According to the fuel fractionation apparatus of the present invention,in the same manner as the fractionation method mentioned above, it ispossible to easily and rapidly control the fuel to the state suitablefor the fractionation. Further, the separation of the fractionated gasphase fuel and liquid phase fuel can be achieved by a simple structure.In this case, the fuel fractionation promoting operation can include anyoperations as far as the operation can promote the vaporization of thefuel, in the same manner as the operation for promoting thefractionation in the fuel fractionation method according to the presentinvention mentioned above.

In the fuel fractionation apparatus of the present invention, an inletof the liquid phase branch passage may be provided with a gas phase fuelin flow inhibiting portion for inhibiting the gas phase fuel fromflowing into a downstream side of the liquid phase branch passage due toan existence of the liquid phase fuel. In this case, even when the gasphase fuel flows into the inlet of the liquid phase branch passage fromthe branch point, it is possible to inhibit the gas phase fuel fromflowing into the downstream side of the liquid phase branch passage bythe gas phase fuel inflow inhibiting portion. Accordingly, it ispossible to securely recover the light component and the heavy componentfrom the respective branch passages in parts. Further, an orifice may beprovided in the gas phase fuel in flow inhibiting portion. Since theliquid phase branch passage is throttled by the orifice in the inletportion, the gas phase fuel is hard to flow into the downstream side ofthe liquid phase branch passage, and it is possible to more securelyseparate the gas phase fuel and the liquid phase fuel in comparison withthe structure having no orifice.

In the fuel fractionation apparatus of the present invention, thefractionation section may extend through an area to which a heatingoperation is applied due to a heat wasted from the internal combustionengine as the fractionation promoting operation. It is unnecessary tosupply an energy required for promoting the fuel fractionation from anexternal portion, by utilizing the heat wasted from the internalcombustion engine as mentioned above.

The fuel fractionation apparatus of the present invention may utilize anexhaust heat of the internal combustion engine as the heat wasted fromthe internal combustion engine. In this case, it is possible to promotethe fractionation by heating the fuel passing through the fractionationsection by the exhaust heat.

The fuel fractionation apparatus of the present invention may comprise apressure regulating device for regulating a pressure within thefractionation passage as a device for generating the fractionationpromoting operation. It is possible to lower a boiling point of the fuelby lowering the pressure within the fractionation passage. Accordingly,it is possible to promote the vaporization of the fuel so as to promotethe fractionation by regulating the pressure.

The fuel fractionation apparatus of the present invention may comprise apressure control device for controlling an operation of the pressureregulating device based on a temperature of the fuel flowing through thefractionation passage. When the temperature of the fuel flowing throughthe fractionation passage is lower than the boiling point of the fuelunder the atmospheric pressure, the fuel is hard to be vaporized. Inthis case, it is possible to promote the vaporization of the fuel bylowering the pressure within the fractionation passage so as to lowerthe boiling point of the fuel. It is possible to maintain afractionation performance of the fractionation passage in a constantdesirable state, by regulating the pressure within the fractionationpassage even at the temperature at which the fuel is hard to bevaporized.

The fuel fractionation apparatus may comprise a temperature detectingdevice for detecting a temperature of the branch point, a temperatureadjusting device capable of adjusting the temperature of the branchpoint, and a temperature control device for controlling an operation ofthe temperature adjusting device based on the temperature detected bythe temperature detecting device such that the temperature of the branchpoint is maintained at a predetermined target temperature. In this case,it is possible to maintain the temperature at the branch point to thetarget temperature so as to hold a separating performance between thelight component and the heavy component in a constant desirable state.In this case, the target temperature is approximately set incorrespondence to various conditions such as a component of the lightcomponent to be vaporized.

In the fuel fractionation apparatus of the present invention, thetemperature adjusting device may change a flow rate of the fuelconducted to the fractionation section so as to adjust the temperatureof the branch point. Since the temperature of the fuel reaching thebranch point is determined based on a heat amount applied from theexhaust gas in the fractionation section and a flow rate of the fuelpassing through the fractionation section, it is possible to adjust thetemperature at the branch point by changing the flow rate of the fuelconducted to the fractionation section. Accordingly, it is possible toadjust the temperature at the branch point to a desired range based on asimple structure such as a flow rate adjusting valve.

In the fuel fractionation apparatus of the present invention, thetemperature control device may operate the temperature adjusting devicesuch that the flow rate of the fuel conducted to the fractionationsection is limited to a minimum value when the temperature detected bythe temperature detecting device deflects from an allowable range withrespect to the target temperature. When the temperature at the branchpoint is low, the fuel of the light component is not vaporized, or isvaporized only at a small amount, it is supposed that the lightcomponent reaches the branch point in the liquid phase together with theheavy component even when the fuel is introduced to the fractionationsection. On the other hand, when the temperature at the branch point ishigh, there is a risk that even the heavy component is vaporized. On thecontrary, it is possible to inhibit the light component and the heavycomponent from being mixed, by setting an allowable range in thetemperature at the branch point and inhibiting the flow rate to theminimum value when the temperature deflects from the allowable range. Inthis case, the minimum value may be 0, or may be an optional value whichis larger than 0. In other words, the aspect inhibiting the flow rate tothe minimum includes both of a case where the fuel is not introduced tothe fractionation section by stopping the supply of the fuel, and a casewhere the fuel is supplied to the fractionation section and the flowrate is limited to an adjustable minimum value.

The fuel fractionation apparatus may comprise a distillation fuelcontainer for accumulating the fuel conducted from the gas phase branchpassage, and an accumulation volume detecting device for detecting anaccumulation volume of the distillation fuel container, and thetemperature control device may lower the target temperature with theaccumulation volume detected by the accumulation volume detecting deviceincreasing. When the fuel in the gas phase is accumulated much in theaccumulation volume, it is possible to conduct only the light fuelhaving a lower boiling point to the gas phase branch passage by loweringthe target temperature. On the other hand, when the accumulation volumeis small, it is possible to increase a yield of the vaporized componentby increasing the target temperature, thereby quickly increasing theaccumulation volume.

In the fuel fractionation apparatus of the present invention, thefractionation section may be provided within the exhaust passage of theinternal combustion engine, and the branch point may be provided in anouter side of the exhaust passage. In this case, since the fractionationsection is provided within the exhaust passage, it is possible toeffectively carry out heat exchange between the exhaust gas and thefuel. On the other hand, since the branch point is provided in the outerside of the exhaust passage, it is possible to make an influence whichthe temperature fluctuation of the exhaust gas applies to thetemperature fluctuation at the branch point small, and it is possible tomore easily control the temperature at the branch point.

In the fuel fractionation apparatus of the present invention, an exhaustgas purifying device may be provided in the exhaust passage of theinternal combustion engine, and the fractionation section may beprovided so as to carry out heat exchange between the fractionationsection and the exhaust passage in a downstream side of the exhaust gaspurifying device. In this case, since the temperature fluctuation of theexhaust gas is absorbed by heat absorption and heat generation by theexhaust gas purifying device, it is possible to more easily control thetemperature in the fractionation section and the branch point in thedownstream side thereof. When the temperature of the exhaust gaspurifying device is controlled to a predetermined temperature range, itis possible to further easily control the temperature at the branchpoint, and it is possible to control the temperature at the branch pointby utilizing an apparatus for controlling the temperature of the exhaustgas purifying device.

In the fuel fractionation apparatus of the present invention, thefractionation section may be provided so as to carry out heat exchangebetween the fractionation section and an engine main body surrounding acombustion chamber in the internal combustion engine or a cooling waterof the engine main body. During an operation of the internal combustionengine, the engine main body surrounding the combustion chamber iscooled by the cooling water, and is kept at an approximately fixedtemperature. Further, since a heat capacity of the cooling water islarger than the gas, the temperature thereof is not rapidly changed.Accordingly, it is possible to stably supply the heat to thefractionation section by arranging the fractionation section so as toexchange the heat with the engine main body or the cooling waterthereof. Therefore, it is possible to stably fractionate the fuel.

In the fuel fractionation apparatus of the present invention, anintended use of the separated gas phase fuel (the light component) andthe liquid phase fuel (the heavy component) is not limited, however, asa preferable aspect of the intended use, there can be listed up astructure that the light component is added as a reducing agent to anNOx occlusion-reduction type catalyst. In this case, a reaction of thereducing agent within the catalyst is improved and a reductionefficiency of the NOx is improved. Further, since the light reducingagent has an improved evaporating property, it is possible to inhibit acatalyst front end face from being closed due to an attachment of thereducing agent to the catalyst by using the light component.

As is discussed in the above, according to the present invention, sincethe operation for promoting the fractionation is applied to thefractionation passage while the fuel is conducted in the fractionationpassage, the response of the fuel to the operation for promoting thefractionation becomes sensitive in comparison with the case where alarge amount of fuel accumulated in the fixed portion is fractionatedall at once, and it is possible to easily and rapidly control the fuelto the state suitable for the fractionation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a first embodiment of a fractionation apparatusaccording to the present invention;

FIG. 2 is a view showing a part of the fractionation apparatus in FIG. 1in an enlarged manner;

FIG. 3 is a flow chart showing a procedure of an open-close controlroutine which an ECU of the fractionation apparatus in FIG. 1 executes;

FIGS. 4A and 4B are views showing a target temperature used in theopen-close control routine in FIG. 3 and a switching action of a valvein the open-close control routine in FIG. 3;

FIG. 5 is a view showing a second embodiment of the fractionationapparatus according to the present invention;

FIG. 6 is a view showing a third embodiment of the fractionationapparatus according to the present invention;

FIG. 7 is a view showing a part of the fractionation apparatus in FIG. 6in an enlarged manner;

FIG. 8 is a view showing another example in the third embodimentaccording to the present invention;

FIG. 9 is a flow chart showing a pressure control routine which an ECUin FIG. 8 executes;

FIG. 10 is a view showing an example in which an orifice is provided inan inlet of a liquid phase fuel branch passage; and

FIG. 11 is a view showing a modified embodiment of a liquid phasepassage of the fractionation apparatus in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 shows an embodiment in which a fuel fractionation apparatusaccording to the present invention is applied to a diesel engine 1 as aninternal combustion engine. An intake passage 2 and an exhaust passage 3are connected to the engine 1. In the intake passage 2, there areprovided a compressor 4a of a supercharger 4 which increases an intakepressure by utilizing an exhaust energy, and a throttle valve 5 foradjusting volume of intake air, and there are provided in a side of theexhaust passage 3 a turbine 4 b of the supercharger 4 arranged in adownstream side of a manifold 3 a, and an exhaust gas purifyingapparatus 6 arranged in a downstream side from the turbine 4 b,respectively. The exhaust gas purifying apparatus 6 is a known structurein which an occlusion-reduction type NOx catalyst material is carried,for example, by a filter substrate for collecting particulate. In thiscase, an aspect of the occlusion of NOx is not limited as far as NOx canbe held.

The engine 1 is provided with a fuel tank 7 for accumulating a fuel (agas oil), a feed passage 8 extending from the fuel tank 7, a highpressure pump 9 for feeding the fuel in the fuel tank 7 to an injector(not shown) via a feed passage 8, and a return passage 10 branched fromthe feed passage 8 in a downstream side of the high pressure pump 9 andprovided for returning a surplus fuel in the fed fuel to the fuel tank7.

An operation state of the engine 1 is controlled by an engine controlunit (ECU) 11. The ECU 11 is structured as a computer obtained bycombining a microprocessor and a peripheral device such as ROM, RAMserving as a main memory device, and the like, and controls theoperation state of the engine 1 by adjusting a fuel injection amount orthe like with reference to an output signals from various sensors.

The engine 1 is provided with a fractionation apparatus 20 forfractionating the fuel in the fuel tank 7. The fractionation apparatus20 is provided with a fractionation passage 21 connected to the returnpassage 10, and a liquid phase passage 22 and a gas phase passage 23which are branched from the fractionation passage 21.

As also shown in FIG. 2, the fractionation passage 21 reaches a branchpoint 21 c via a fractionation section 21 a and a horizontal portion 21b. The fractionation section 21 b passes obliquely within the exhaustpassage 3 in an upstream side of the exhaust gas purifying apparatus 6while being inclined with respect to a horizontal direction. Thehorizontal portion 21 b and the branch point 21 c are provided in anouter side of the exhaust passage 3. The fractionation passage 21extends toward a lower side as a whole, and a fuel (a liquid phase fuel)f1 supplied from the return passage 10 flows toward the branch point 21c due to gravity.

The liquid phase passage 22 has a gas phase stagnation portion (a gasphase fuel inflow inhibiting portion) 22 a vertically extending from thebranch point 21 c to a lower side, and a passage portion 22 b extendingin a horizontal direction from the gas phase stagnation portion 22 a. Aninner diameter of the passage portion 22 b is set to be slightly smallerthan the inner diameter of the gas phase stagnation portion 22 a. Adownstream side of the passage portion 22 b is connected to a positionwhich can return the fuel to the fuel tank 7. For example, the passageportion 22 b may be directly connected to the fuel tank 7, or may beconnected to the return passage 10 in a downstream side from a positionto which the fractionation passage 21 is connected.

The gas phase passage 23 extends in a horizontal direction from thebranch point 21 c, a downstream side of the gas phase passage 23 isconnected to a distillation fuel container 24 for accumulating a lightcomponent fuel as shown in FIG. 1, and a fractionated gas phase fuel f2is conducted to the distillation fuel container 24 based on a pressurewithin the fractionation passage 21 and the gas phase passage 23. Inthis, case, each of the passages 21 to 23 may be formed by anappropriate material, and may employ, for example a metal pipe.

The fractionation apparatus 20 shown in FIG. 1 is further provided witha valve 25 corresponding to a temperature adjusting device, atemperature sensor 26 corresponding to a temperature detecting device,and an accumulation volume detecting sensor 27 corresponding to anaccumulation volume detecting device. The valve 25 is provided as anelectromagnetic valve which can open and close a connection portionbetween the return passage 10 and the fractionation passage 21, and amotion of the valve 25 is controlled by the ECU 11 corresponding to atemperature control device. The temperature sensor 26 is provided in thebranch point 21 c, and outputs a signal in correspondence to a detectedtemperature to the ECU 11. The accumulation volume detecting sensor 27detects an accumulation volume of the distillation fuel container 24 andoutputs a signal in correspondence to a detected accumulation volume.

The engine 1 is additionally provided with an adding apparatus 28 foradding the fuel accumulated in the distillation fuel container 24 to anupstream side of the exhaust gas purifying apparatus 6 so as to serve asa reducing agent. The adding apparatus 28 is structured such as toinclude, for example, an adding feed passage 29 connected to thedistillation fuel container 24, an adding feed pump 30 for sucking thefuel in the distillation fuel container 24 to the adding feed passage29, and an adding injector 31 for injecting the reducing agent to theexhaust passage 3.

A description will be given of an operation of the fractionationapparatus 20 having the structure mentioned above. FIG. 3 is a flowchart showing a procedure of an open-close control routine which the ECU11 executes for controlling a switching action of the valve 25. Theroutine is executed repeatedly at a predetermined cycle (for example,0.5 second) during the operation of the engine 1.

The ECU 11 first determines based on the accumulation volume detected bythe accumulation volume detecting sensor 27 whether or not thedistillation fuel container 24 is filled (step S1). When the ECU 11determines that it is filled, the ECU 11 fully closes the valve 25 (stepS11) and terminates the process. When the ECU 11 determined that it isnot filled, the ECU 11 sets a target temperature of the branch point 21c in correspondence to an accumulation volume (step S2). At this time,as shown in FIG. 4A, the ECU 11 sets such that the more the accumulationvolume is, the lower the target temperature becomes. The targettemperature may be appropriately set in correspondence to a component ofthe fuel to be obtained according to the fractionation, however, may beset in a range, for example, around 220° C. In this case, in FIG. 4A,there is exemplified a case where the target temperature is lowered at aconstant rate of change with respect to an increase of the accumulationvolume, however, the rate of change may be changed with respect to theaccumulation volume. In step S1, it is determined whether or not thedistillation fuel container 24 is filled, however, may be determinedwhether or not the distillation fuel container 24 is equal to or morethan an optional predetermined amount less than an accumulation volumeat a fill time.

In steps S3 and S4 in FIG. 3, the ECU 11 determined whether or not thetemperature detected by the temperature sensor 26 is lower than a lowerlimit value of an allowable range with respect to the targettemperature, and whether or not it is higher than an upper limit valueof the allowable range. When ECU 11 determines that it is lower than thelower limit value or higher than the higher limit value, the ECU 11fully closes the valve 25 (step S11), and terminates the process. Whenthe ECU 11 determines that it is within the allowable range, the ECU 11goes to step S5. When the ECU 11 executes the processes of steps S3 andS4, whereby the detected temperature does not exist in a range between alower limit value Tmin and an upper limit value Tmax, as shown bystraight lines L1 and L3 in FIG. 4B, the valve 25 is closed. In thiscase, the lower limit value and the upper limit value of the allowablerange may be appropriately set with respect to the target temperature,however, a temperature at which a yield of the light component to beobtained is approximately 0 may be set as the lower limit value.

In step S5 in FIG. 3, the ECU 11 determined whether or not the valve 25is fully closed, and when the ECU 11 determines that it is fully closed,the ECU 11 controls a motion of the valve 25 so as to open the valve 25up to a predetermined opening degree (step S6). In this case, an openingdegree at this time may be set by determining an opening degree whichcan quickly make the temperature of the branch point 21 c to the targettemperature, based on conditions such as the target temperature, thetemperature detected by the temperature sensor 26, the operation stateof the internal combustion engine and the like. When the ECU 11determines in step S5 that the valve 25 is not fully closed, the ECU 11skips step S6 and goes to step S7.

After step S7, the ECU 11 controls an opening degree of the valve 25based on the temperature detected by the temperature sensor 26 such thatthe temperature at the branch point 21 c reaches the target temperatureso as to adjust a flow rate of the fuel flowing into the fractionationpassage 21. The opening degree of the valve 25 may be controlledaccording to various control methods, however, may be controlled in amanner as shown in steps S7 to S10.

Instep S7, the ECU 11 determines whether or not the detected temperatureis equal to the target temperature, and when the ECU 11 determined thatthey are equal, the ECU 11 terminates the process. When the ECU 11determines that they are not equal, the ECU 11 determines whether or notthe detected temperature is higher than the target temperature (stepS8). When the ECU 11 determines that it is higher than the targettemperature, the ECU 11 increases the opening degree of the valve 25 atonly an amount in correspondence to a difference between the detectedtemperature and the target temperature (step S9), and terminates theprocess. When the ECU 11 determines that the detected temperature is nothigher than the target temperature, the ECU 11 reduces the openingdegree of the valve 25 at an amount in correspondence to the differencebetween the detected temperature and the target temperature (step S10),and terminates the process. According to the process of steps S7 to S10,as shown by a straight line L2 in FIG. 4B, the valve 25 is controlledsuch that the opening degree is in proportion to the detectedtemperature. Accordingly, the detected temperature converges into atarget temperature Ts. In this case, it is possible to employ adifferential control and an integral control such that the detectedtemperature quickly or accurately converges into the target temperatureTs, or it is possible to forecast the change of the exhaust gastemperature based on various conditions such as the operation state ofthe engine 1 and the like, thereby changing the flow rate of thefractionation passage 21 before the temperature of the branch point 21 cis changed.

In the present embodiment, the return fuel from the injector isintroduced to the fractionation passage 21 via the return passage 10.Since the temperature of the return fuel from the injector increases upto about 150° C. and the temperature thereof is higher than that of thefuel in the fuel tank 7, it is possible to quickly increase thetemperature up to the fractionation temperature in the fractionationsection 21 a.

Further, in the present embodiment, the target temperature is set around220° C. Since a boiling point of benzothiophene having a lowest boilingpoint in a sulfur content left in a low sulfur gas oil (equal to or lessthan 50 ppm) is 220° C., the fuel obtained via the gas phase passage 23contains no sulfur content or hardly contains the sulfur content byfractionating at a temperature equal to or less than that temperature.Therefore, in the present embodiment, it is possible to obtain mainlythe fuel in which no sulfur content is obtained. In this case, the fuelcontaining no sulfur content has various usability. For example, whenthe gas oil in which no sulfur content is contained is added as thereducing agent to the exhaust passage 3, it is possible to prevent theexhaust gas purifying apparatus 6 from being poisoned by the sulfur.

Second Embodiment

The second embodiment according to the present invention is shown inFIG. 5. In this case, in the present embodiment, the same referencenumerals are attached to the common parts with the first embodiment, anda detailed description thereof will be omitted. In the presentembodiment, the exhaust gas purifying apparatus 6 is providedcomparatively near the turbine 4 b, and the fractionation section 21 ais provided so as to pass through the exhaust passage 3 in thedownstream side of the exhaust gas purifying apparatus 6. Further, theadding injector 31 is provided in the manifold 3 a. In the presentembodiment, the NOx occlusion-reduction type catalyst is controlled andoperated at 250 to 400° C. so as to effectively function. Accordingly,it is easy to control the temperature of the branch point 21 c to thefractionation temperature 220° C. so as to obtain the fractionated fuelcontaining no sulfur.

Third Embodiment

The third embodiment according to the present invention is shown in FIG.6. Further, FIGS. 7A and 7B show views obtained by enlarging a part ofthe fractionation apparatus 20 in FIG. 6. In this case, FIG. 7A shows aplan view of the cylinder head 1 a of the internal combustion engine 1in FIG. 6, and FIG. 7B shows a view in the case of seeing a crosssection of the cylinder head la along a line VII-VII in FIG. 7A from aside of the manifold 3 a. In this case, in the present embodiment, thesame reference numerals are attached to the common portions with thoseof the first embodiment, and a detailed description thereof will beomitted. As is apparent from FIGS. 6, 7A and 7B, the present embodimentis different from the other embodiments in points that the fractionationpassage 21 is arranged within the cylinder head la corresponding to theengine main body surrounding the combustion chamber of the engine 1, anda pressure reducing pump 32 is provided as a pressure regulating devicefor regulating the pressure within the fractionation passage 21 in thegas phase passage 23. The cylinder head la is cooled even under theoperation of the engine 1, and the temperature thereof is maintained ata temperature equal to or less than a predetermined temperature lowerthan the fractionation temperature. Accordingly, the pressure within thefractionation passage 21 is reduced by the pressure reducing pump 32,thereby lowering the boiling point of the fuel and promoting thevaporization of the fuel.

In the present embodiment, since the fractionation passage, 21 isarranged in the cylinder head la having a stable temperature, it ispossible to stably supply the heat to the fractionation passage 21.Accordingly, it is possible to stabilize a nature of the fractionatedgas phase fuel. In this case, it is possible to further promote thefractionation of the fuel by arranging the fractionation passage 21 inthe side of the exhaust port which has a higher temperature in thecylinder head 1 a. Further, since the fractionation passage 21 can beprovided within the cylinder head la only based on an additional work,it is possible to inhibit the number of the parts of the fractionationapparatus 20 from being increased, and it is possible to reduce a cost.

In the present embodiment, the place in which the fractionation passage21 is arranged is not limited to the engine main body of the engine 1.For example, the fractionation passage 21 may be provided such that theheat can be exchanged between the cooling water of the engine 1 and thefractionation passage 21. Further, as shown in FIG. 8, the fractionationpassage 21 may be provided such that the fractionation section 21 aextends through the exhaust passage 3.

When the exhaust gas temperature is low such as just after starting theengine 1, the temperature of the fuel flowing through the fractionationpassage 21 does not rise up to the fractionation temperature, so thatthe fuel is hard to be vaporized. In the embodiment in FIG. 8, thepressure within the fractionation passage 21 is lowered by operating thepressure reducing pump 32 provided in the gas phase passage 23 in thecase mentioned above, whereby the boiling point of the fuel is loweredand the vaporization of the fuel is promoted. The operation of thepressure reducing pump 32 is controlled by the ECU 11. FIG. 9 is a flowchart showing a pressure control routine which the ECU 11 executes forcontrolling the operation of the pressure reducing pump 32 in FIG. 8.The control routine in FIG. 9 is executed repeatedly at a predeterminedcycle during the operation of the engine 1. The ECU 11 serves as thepressure control device by executing the control routine in FIG. 9.

In the control routine in FIG. 9, the ECU 11 first determines in stepS21 whether or not a temperature of the fuel flowing within thefractionation passage 21 is lower than a target temperature. Thetemperature of the fuel can be estimated based on a temperature inconnection with the fractionation of the fuel, such as the temperaturedetected by the temperature sensor 26 or an exhaust gas temperaturesensor 33 outputting a signal in correspondence to the temperature ofthe exhaust gas, or the like. When the ECU 11 determines that thetemperature of the fuel is not low, the ECU 11 finishes this timecontrol routine.

On the other hand, when the ECU 11 determines that the temperature ofthe fuel is low, the ECU 11 goes to step S22, and operates the pressurereducing pump 32 so as to regulate the pressure within the fractionationpassage 21. Since the boiling point of the fuel is lowered according tothe reduction of the pressure, the ECU 11 controls the operation of thepressure reducing pump 32 such as to lower the pressure within thefractionation passage 21 according to the lower temperature of the fuel.Thereafter, the ECU 11 terminates this time control routine.

By regulating the pressure within the fractionation passage 21, it ispossible to stably gasify the fuel even when the exhaust gas temperatureof the engine 1 is low. Further, it is possible to set a condition bywhich only the light component fuel is vaporized, by regulating thepressure within the fractionation passage 21 so as to adjust the boilingpoint of the fuel. Accordingly, it is possible to stabilize the natureof the gas phase fuel. In this case, in the embodiment in FIG. 8, theECU 11 may execute the open-close control routine of the valve 25 inFIG. 3 in parallel to the pressure control routine in FIG. 9, therebyregulating the pressure within the fractionation passage 21 and thetemperature at the branch point 21 c.

The present invention is not limited to the embodiments mentioned above,and may be carried out according to various aspects within the technicalscope of the present invention. For example, the energy of the internalcombustion engine utilized for promoting the fractionation of the fuelis not limited to the heat energy wasted from the internal combustionengine such as the exhaust heat or the like. It is possible to utilizeany energy generated based on the operation of the internal combustionengine for promoting the fractionation.

The fractionation section 21 a may be provided so as to carry out heatexchange between the section 21 and an appropriate position of theexhaust passage 3, for example, may be provided so as to extend throughan inner side of the manifold 3 a. In this case, since the fractionationsection 21 a is provided at the position having the higher exhaust gastemperature, it is possible to quickly increase the temperature of thefuel.

The gas phase stagnation portion 22 a and the passage portion 22 b maybe formed in an appropriate shape as far as it is possible to close thedownstream side of the gas phase stagnation portion 22 a by the liquidphase fuel. As shown in FIG. 10, the structure is such that an innerdiameter of the liquid phase passage 22 is reduced by adding an orifice22 c in the middle of the gas phase stagnation portion 22 a. In thiscase, the gas phase fuel is hard to flow into the downstream side fromthe orifice 22 c, and it is possible to securely inhibit the gas phasefuel from flowing into the downstream side of the liquid phase passage22. As shown in FIG. 11, the gas phase stagnation portion 22 a and thepassage portion 22 b may be formed by forming the liquid phase passage22 in a S-shaped bent shape.

The fractionation passage 21 may be connected to an appropriate positionof the fuel supply system, for example, may be connected to the feedpassage 8 or may be connected to the fuel tank 7.

The target temperature may be appropriately set in correspondence to thevaporized light component. For example, the target temperature is notlimited to the range around 220° C., and the target temperature may beset in correspondence to the accumulation volume of the distillationfuel container 24 within the range equal to or less than 220° C., or maybe fixed to 220° C. or the temperature near 220° C.

1. A fuel fractionation method for an internal combustion enginecomprising the steps of: applying an operation for promoting afractionation of a fuel of the internal combustion engine to afractionation passage while making the fuel flow to the fractionationpassage, thereby fractionating the fuel into a gas phase fuel and aliquid phase fuel within the fractionation passage; conducting thefractionated gas phase fuel and the fractionated liquid phase fuel to abranch point of the fractionation passage; and separating the gas phasefuel and the liquid phase fuel to an upper branch passage and a lowerbranch passage, respectively due to gravity.
 2. A fuel fractionationapparatus for an internal combustion engine comprising: a fractionationpassage which is connected to a fuel supply system of the internalcombustion engine and reaches a branch point of a terminal end through afractionation section to which a fractionation promoting effect of afuel is applied; a liquid phase branch passage which is branched to alower side from the branch point; and a gas phase branch passage whichis branched to an upper side than the liquid phase branch passage fromthe branch point.
 3. The fuel fractionation apparatus according to claim2, wherein an inlet of the liquid phase branch passage is provided witha gas phase fuel inflow inhibiting portion for inhibiting the gas phasefuel from flowing into a downstream side of the liquid phase branchpassage due to an existence of the liquid phase fuel.
 4. The fuelfractionation apparatus according to claim 3, wherein an orifice isprovided in the gas phase fuel inflow inhibiting portion.
 5. The fuelfractionation apparatus according to claim 2, wherein the fractionationsection extends through an area to which a heating operation is applieddue to a heat wasted from the internal combustion engine as thefractionation promoting operation.
 6. The fuel fractionation apparatusaccording to claim 5, wherein an exhaust heat of the internal combustionengine is utilized as the heat wasted from the internal combustionengine.
 7. The fuel fractionation apparatus according to claim 2,comprising a pressure regulating device for regulating a pressure withinthe fractionation passage as a device for generating the fractionationpromoting operation.
 8. The fuel fractionation apparatus according toclaim 7, comprising a pressure control device for controlling anoperation of the pressure regulating device based on a temperature ofthe fuel flowing through the fractionation passage.
 9. The fuelfractionation apparatus according to claim 5, comprising: a temperaturedetecting device for detecting a temperature of the branch point; atemperature adjusting device capable of adjusting the temperature of thebranch point; and a temperature control device for controlling anoperation of the temperature adjusting device based on the temperaturedetected by the temperature detecting device such that the temperatureof the branch point is maintained at a predetermined target temperature.10. The fuel fractionation apparatus according to claim 9, wherein thetemperature adjusting device changes a flow rate of the fuel conductedto the fractionation section so as to adjust the temperature of thebranch point.
 11. The fuel fractionation apparatus according to claim10, wherein the temperature control device operates the temperatureadjusting device such that the flow rate of the fuel conducted to thefractionation section is limited to a minimum value when the temperaturedetected by the temperature detecting device deflects from an allowablerange with respect to the target temperature.
 12. The fuel fractionationapparatus according to claim 10, comprising: a distillation fuelcontainer for accumulating the fuel conducted from the gas phase branchpassage; and an accumulation volume detecting device for detecting anaccumulation volume of the distillation fuel container, wherein thetemperature control device lowers the target temperature with theaccumulation volume detected by the accumulation volume detecting deviceincreasing.
 13. The fuel fractionation apparatus according to claim 5,wherein the fractionation section is provided within the exhaust passageof the internal combustion engine, and the branch point is provided inan outer side of the exhaust passage.
 14. The fuel fractionationapparatus according to claim 5, wherein an exhaust gas purifying deviceis provided in the exhaust passage of the internal combustion engine,and the fractionation section is provided so as to carry out heatexchange between the fractionation section and the exhaust passage in adownstream side of the exhaust gas purifying device.
 15. The fuelfractionation apparatus according to claim 7, wherein the fractionationsection is provided so as to carry out heat exchange between thefractionation section and an engine main body surrounding a combustionchamber in the internal combustion engine or a cooling water of theengine main body.